1. Field of the Invention
The present invention relates to a fan unit including a housing assembly which has a plurality of housings connected to or engaged with each other, and to the housing assembly of the fan unit.
2. Description of the Related Art
In order to improve the high capacity of an air flow and a static pressure generated by a fan without increasing the impeller diameter, a fan unit called “a double fan” is widely used in which a plurality of axial fans are arranged along the rotational axis thereof. Also, another type of fan unit is used which uses centrifugal fans connected in series with a direction in which the air is blown so as to provide a high static pressure.
In an exemplary known fan unit having a plurality of fan impellers, two or more impellers are encased in a single housing or each impeller is encased in each housing, and the housings are connected with each adjoining housing in an axial direction substantially parallel to the rotational axes thereof. Generally, a high development cost is required to design a new fan unit including the design of its housing. Therefore, one way for achieving a cost reduction is to connect or engage a plurality of existing axial fans or centrifugal fans, which meets the performance requested for the new fan unit.
There are two major ways to connect or engage two or more adjoining housings. One way is that flanges of the housings are fixedly coupled to each other by screws, and the other is that elastic hooks formed on one housing are engaged with recesses of the other housing.
In the case where the fans are fixedly connected by screws, however, a special tool such as a screwdriver or wrench may be required. This increases the number of steps for connecting the fans as well as the number of parts of the fan unit, thereby the cost for producing the fan unit may increase because of the complex structure of the fan unit. In connecting the adjoining fans by elastic hooks, on the other hand, since the elastic hooks can be formed at the same time as the housing is formed by a molding process, the cost for the housing with such elastic hooks does not necessarily increase. Also, the elastic hooks can be engaged very simply without increasing the number of steps for engaging the housings.
However, when the connection by elastic hooks is performed, there are two requirements competing with each other. One requirement is to provide a sufficient elasticity for elastic deformation which may be required for engaging the two adjoining fans, and the other requirement is to provide a sufficient engaging force. Specifically, in the case where the elasticity of the elastic hooks is increased to achieve an easier engaging step, the engaging force decreases and an insufficient engaging force may occur. On the other hand, in the case where the elasticity of the elastic hooks is decreased, the engaging force increases but the engaging step becomes difficult because the elastic hooks may be damaged or the housing may be warped.
That is, it is difficult to provide the elastic hooks with an appropriate level of elasticity in the case of using elastic hooks, even though the use of elastic hooks appears to be simple.